Final answer:
The ageing index measures the proportion of older persons to younger populations. An increase in this index indicates an aging society, as shown by figures illustrating the growing percentage of the U.S. population over sixty-five. This demographic shift, also referred to as the 'graying of the United States', affects societal age composition.
Step-by-step explanation:
The ageing index, as mentioned by Gavrilov LA et al., 2003, refers to the ratio or proportion of older persons (age 65 and above) in comparison to younger populations. Specifically, it deals with the proportion of persons aged 0-14, 15-64, and 65 and above. To find the ageing index, one would compare the percentage of the population that is 65 and over with the percentage of the population that is under 14 years of age. An increase in the ageing index signifies a society with a higher proportion of elderly individuals.
Referring to the various figures provided, it is evident that there is a notable trend of growth in the population of individuals who are 65 years and above. For instance, Figure 13.4 highlights the increasing size of the population in the age group of 65-84, indicating the graying of the United States. This term defines the increasing percentage of the population over sixty-five years old.
With regards to the distribution of age demographics, Figure A6 and corresponding Table A4 data show shifts over time among children, working-age adults, and the elderly. This assists in understanding how the ageing index may change over time and informs us about the societal shifts in age composition. As the proportion of individuals aged 65 and above grows, the ageing index will increase, pointing to an aging population.